Actions by the U.S. military across the Afghanistan border into Pakistan have been on the rise throughout the year. Two weeks ago, the new Pakistani Army chief of staff, Gen. Ashfaq Parvez Kayani, publicly stated that additional U.S. activity in Pakistan would be considered hostile — and the Pakistani army would act accordingly. The statement, coming from a major U.S. ally that happens to host an Al Qaeda safe haven on its territory, so disturbed the Bush administration that it dispatched Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, to Islamabad to cool Kayani’s jets.

It appears not to have worked. Early reports are sketchy, but it appears the Pakistani army fired “warning shots” at U.S. helicopters that entered North Waziristan from Afghanistan’s Khost Province. (If the helicopters indeed came from Khost, I wonder if they entered from Forward Operating Base Salerno, the largest U.S. base in Khost, 12 miles from the Pakistani border, where I spent a couple days the week before last.) Reports the BBC:

The latest confrontation between US and Pakistani forces took place in North Waziristan’s sparsely populated Ghulam Khan district, west of the main town in the region, Miranshah, local officials say.

They told the BBC that troops at border posts in the mountainous region fired at two US helicopters which crossed into Pakistani territory.

The helicopters returned to Afghanistan without retaliating.

For U.S. troops to be fired upon by Pakistani troops has to mark a new and rather dangerous phase in the post-Musharraf era, and the war on terrorism broadly.